Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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INJECTION MOLDING OF A TIRE COMPONENT
Back~round o~ the Invention
Manu~acturing automobile and truck tires requires
the preassembly o~ certain tire components, assembling
the components on a tire building machine and
vulcanization o~ the assembled tire components in a
tire press.
Two o~ the components which are made prior to
assembly on the tire building machine are the tire
bead apex assembly and the tire tread. These
components which have been made o~ unvulcanized rubber
are relatively thick and the extra time required to
cure the rubber in them has increased the time
required to cure the tire in the tire press. Also the
uncured apex bead assembly may be distorted during
building of the tire or during transportation o~ the
tire to the tire vulcanizer. The unvulcanized tread
is also subject to distortion during assembly and
vulcanization.
It has been ~ound that the uni~ormity o~ the
cured tire can be improved and the cure time in the
tire press can be reduced by building a tire with
prevulcanized bead apex assemblies and/or a
prevulcanized tread.
Summary o~ the Invention
In accordance with this invention tire components
such as bead apex assemblies and tire treads are
injection molded providing semi-vulcanized tire
components molded to precise ~m~n~ions and requiring
no additional cure time in the tire press. This is
accomplished by injecting an elastomeric material such
as rubber into molds having the shape o~ the component
in the ~inished tire. The time required ~or curing
the injected rubber in the injection molding apparatus
is reduced by increasing the temperature o~ the
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elastomeric material as it is injected through a
narrow gate opening into the mold cavity.
Temperatures o~ the elastomeric material be~ore it
reaches the mold are controlled by heating and cooling
passages leading to a generally circular manifold
adjacent the gate.
By injecting the elastomeric material into a
manifold surrounded by the mold cavity, weld lines in
the molded components can be avoided by locating the
mani~old so that some portions are closer to the mold
cavity than others whereby the pressure at the mold
cavity is equal at all points along the edge o~ the
cavity.
The bead o~ the bead apex assembly may be
supported by blade members in the surface o~ the mold
which form slots in the assembly that are ~illed
during the wlcanization o~ the tire.
The bead apex assembly may be removed ~rom the
mold with an unloading ring by commnn;cating a vacuum
to the ring to hold the bead apex assembly during
removal.
In accordance with an aspect of the invention,
there is provided a method o~ injection molding a
circular tire component comprising:
(a) heating and mixing an elastomeric material;
(b) injecting the elastomeric material into a
plurality o~ runners in a cold block of a mold
assembly;
(c) controlling the temperature of the
elastomeric material in the runners in the cold block;
(d) commlln;cating the elastomeric material ~rom
the runners to a generally circular mani~old in a
heated mold having opposing mating surfaces;
(e) cnmmlln;cating the elastomeric material from
the circular mani~old through a landing area to a mold
cavity and subjecting the material to shear and
contact with the sur~ace o~ the heated mold so as to
increase the temperature o~ the material ~rom 240~F to
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330~F plus or minus 20~F to accelerate the curing o~
the material;
(~) curing the elastomeric material ~or a period
o~ time;
(g) opening the mold; and
(h) removing the tire component ~rom the mold.
In accordance with another aspect o~ the
invention, there is provided an apparatus ~or
injection molding a circular tire component of
elastomeric material comprising:
(a) a mold assembly having a cold block and a
heated mold mounted on the cold block;
(b) an injection apparatus ~or heating, mixing
and injecting the elastomeric material lnto the mold
assembly;
(c) a plurality o~ runners in the cold block ~or
commlln;cating the material ~rom the injection
apparatus to the mold;
(d) a generally circular mani~old de~ined by
opposing ~aces o~ the mold connected to the runners in
the mold;
(e) a mold cavity radially outward o~ the
mani~old de~ined by the opposing ~aces o~ the mold and
(f) a landing area between the mani~old and the
mold cavity de~ined by the opposing sur~aces o~ the
mold and having a narrow opening providing ~or heating
and shearing the material as it is injected into the
mold cavity to increase the temperature and decrease
the curing time o~ the material.
Brie~ Description o~ the Drawings
To acquaint persons skilled in the arts most
closely related to the present invention, certain
pre~erred embodiments thereo~ illustrating best modes
now contemplated for putting the invention into
practice are described herein by and with re~erence to
the annexed drawings ~orming a part o~ the
speci~ication. The embodiments shown and described
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herein are illustrative and as will become apparent to
those skilled in these arts, can be modi~ied in
numerous ways within the spirit and scope o~ the
invention de~ined in the claims hereo~.
In the annexed drawings:
Fig 1 is a fragmentary sectional view with parts
being broken away of a cold block and single apex
assembly mold embodying the invention;
Fig 2 is a ~ragmentary plan view o~ the lower
hal~ o~ the mold shown in Fig 1;
Fig 3 is an enlarged ~ragmentary diagrammatic
view o~ the mold shown in Fig 1 illustrating the
blades ~or supporting and positioning the bead;
Fig 4 iS an enlarged view in section like Fig 1
showing the mani~old, landing and injection passage
into the mold cavity;
Fig 5 is a ~ragmentary plan view like Fig 2
showing a modi~ied mani~old and l~n~ng ~or the lower
mold hal~ to provide for an equal drop in pressure
~rom the mold inlets to the mold cavity;
Fig 6 is a schematic elevation in section o~ a
screw type injection molding apparatus ~or a tire
tread mold shown in the m~ng position o~ the
extruder barrel;
Fig 7 is a view like Fig 6 showing the apparatus
with the extruder barrel in the charging position;
Fig 8 is a plan view o~ the distribution plate
and cold plate illustrating the cold runner system
taken along line 8-8 in Fig 6;
Fig 9 is a fragmentary cross-section o~ the
nozzle, cold plate assembly, and sprue plate o~ the
apparatus shown in Figs 7 and 8 taken along the plane
o~ line 9-9 in Fig 8 showing one o~ the tubes with the
cooling passages;
Fig 10 is an end view o~ the tube taken along
line 11-11 in Fig 9 with parts being broken away;
Fig 11 is a enlarged view in section like Fig 4
showing the mani~old landing and narrow opening at the
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injection yate $or the tread mold shown in Fig 9;
Fig 12 is a fragmentary sectional view of a
plurality of stacked mold plates for simultaneous
injection of a plurality of bead apex assemblies
utilizing the injection molding apparatus of Figs 6
and 7;
Fig 13 is a plan view of the bottom mold plate of
the assembly shown in Fig 12 illustrating the manifold
and l~n~;ng;
Fig 14 is a schematic sectional view showing an
unloader for the bead apex assembly.
Referring to Figs 1,2,3 and 4 a mold assembly 10
is shown having a heated lower mold half 12 and a
heated upper mold half 14 providing a mold cavity 16
for injection molding a circular tire component such
as a bead apex assembly 18.
The mold assembly 10 is mounted on a sprue plate
20 which is fastened to a cold block 22 having cooling
passages 24. The cold block 22 may be mounted on an
inlet block (not shown) for engagement with an
injection molding apparatus and commnn;cates an
elastomer under pressure to a distribution block 28
through an inlet passage 30. Circumferentially spaced
radially extending runners 32 commlln;cate the
elastomer under pressure from the distribution block
28 to nozzles 34 in engagement with circumferentially
spaced sprues 36 in the sprue plate 20. The number of
runners 32 may vary and in this embodiment there are
six runners. Passages 38 in the upper mold half 14
are connected to the sprues 36 and c~mm~ln;cate the
elastomer under pressure to a generally circular
manifold 40 in the lower mold half 12. An enlarged
cross-section of the manifold 40 is shown in Fig 4.
Between the manifold 40 and the mold cavity 16 there
is provided a circular landing area 42 on the lower
mold half 12 which defines an injection passage 44
with the opposing faces of the upper mold half 14.
The injection passage 44 extends radially outward into
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the mold cavity 16. A raised circular rib 46 iS
positioned on the l~n~;ng area 42 ~or ~urther
restricting ~low of the elastomer through the passage
44 and thereby increase the temperature o~ the
material due to exposure to the heated sur~aces o~ the
upper mold hal~ 14 and lower mold hal~ 12 and due to
the shearing of the material. This may increase the
temperature o~ the material ~rom 240~F (115 C) to
330~F (165~C) + - 20~F or (+ - 11~C). The increased
temperature increases rate o~ the curing o~ the
elastomer which reduces the curing time the bead apex
assembly 18 need be held in the mold assembly 10.
The elastomeric material is pre~erably cured ~or
a predetermined length o~ time past the blow point o~
the material upon removal ~rom the component ~rom the
mold. On the Rheometer scale this is around T-25.
Re~erring to Figs 2 and 3 circum~erentially
spaced support blades 4 8 are mounted on the lower mold
halE 12 and upper mold half 14 at the radially inner
suri~ace o~ the mold cavity 16 to support a bead bundle
50 as the mold assembly 10 is closed. The blades 48
support the bead bundle 50 at a position spaced ~rom
the sur~ace o~ the mold cavity 16 so that when the
elastomer is injected into the mold cavity the inner
diameter 52 o:E the bead bundle is uni~ormly coated. A
~lipper normally used to separate the bead wires ~rom
the ply wires in a tire may also not be required. The
rounded inside contour o~ the bead bundle 50 also
allows the ply wires to move uni~ormly during shaping.
In addition the support blades 48 place the bead
bundle 50 in position so that injection against the
inner diameter ~ace o~ the bead will place the bead in
tension and prevent kinking o~ the wires in the bead
bundle. AS shown in Fig 2 each oi~ the support blades
48 is positioned at an angle ~ o~ 45 degrees to the
radius R o~ the mold assembly 10. In this position o~
the blades 48 the resultlng grooves in the bead apex
assembly 18 extend in a direction other than the
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direction of the ply cords wrapped around the bead
apex assembly 18 in a tire built with this assembly so
that the cords of the plies will not be pulled into
the grooves. The support blades 48 are also tapered
to facilitate removal of the bead apex assembly 18
from the lower mold half 12 and upper mold half 14
upon opening of the mold assembly 10.
Referring to Fig 5 a modified lower mold half 54
having a modified manifold 56 is shown. Where the
parts are the same as in the assembly 18 shown in Figs
1,2,3 and 4 they will be identified with the same
number and a prime mark. Runner inlets 58 are at
circumferentially spaced positions corresponding to
the positions of the nozzles 34 shown in Fig 1. Each
of the inlets 58 is the same radial distance from the
edge of the mold cavity 16'. The manifold 56 is
inclined from a circular configuration shown by line C
to radially outward positions P between the inlets 58.
The location of the manifold positions P is half way
between the inlets 58 and closer to the mold cavity
16' by a distance sufficient to provide an elastomeric
pressure at the mold cavity 16' which is substantially
equal to the pressure at the edge of the mold cavity
at positions T which are radially outward from inlets
58.
In between the inlets 58 and positions P the
manifold positions Q,R, and S are also closer to the
mold cavity 16' than the inlets 58 by distances to
provide substantially equal elastomeric pressure at
the edge of the mold cavity 16'. The radial locations
of the manifold positions Q,R, and S can be calculated
by det~rm;n;ng the pressure drop per inch of
elastomeric material passing through the manifold 56
and the pressure drop per inch of material passing
through the injection passage 44'. The pressure drop
at "T" can be determined by multiplying the distance U
between the runner inlets 58 and the edge of the
cavity 16' times the pressure drop per inch in the
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injection passages 44'. This same pressure is then
provided at positions corresponding to Q,R, and S by
locating the manifold 56 in a radial position relative
to the cavity 16' so that the sum of the pressure drop
in the mani~old 56 and the pressure drop in the
injection passage 44' equals the pressure drop at
position T. Therefore, by locating the manifold 56 as
indicated the injection pressure at all positions
around the cavity 16' will be substantially the same
and weld lines in the injected tire component such as
bead apex assembly 18 will be substantially
eliminated.
With re~erence to Figs 6 and 7, a manifold
injection molding apparatus 65 :~or injection molding a
tire component of elastomeric material such as a
rubber tread is shown in the mixing position (Fig 6)
and injection position (Fig 7). A segmented tread
mold 68 has a moving mold plate 70 mounted on a moving
piston plate 72 connected to a mold cylinder 74 ~or
clamping the mold 68 between the mold plate 70 and a
~ixed press plate 76. The segmented tread mold 68
includes a core 78, a heel block 80, a plurality of
radially movable mold segments 82, a sprue plate 84, a
cold plate 86 and a distribution block 88.
A nozzle barrel 90 is mounted on the ~ixed press
plate 76 and has an extruder cylinder 92 slidably
movable in the barrel between the mixing position
shown in Fig 6 and the injection position shown in Fig
7. The extruder cylinder 92 iS part o~ an extruder 94
having an extruder screw 98. The extruder 94 is
mounted on double acting cylinders 100 containing
pistons (not shown) connected to piston rods 102
fastened to the fixed press plate 76 whereby the
extruder 94 and extruder cylinder 92 can be moved
toward and away from the tread mold 68.
As shown more clearly in Fig 9, circumferentially
spaced ports 103 in the distribution block 88 extend
from the centrally located cavity 124 to tubes 125
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having ch~nn~l S 104 in commlln;cation with spring
loaded mold nozzles 106 abutting a sprue plate sur~ace
107 and surrounding openings 108 which are in
cnmmlln;cation with a generally circular mani~old 109
in the sprue plate 84.
As shown in Fig 11 the mani~old 109 is in
commlln;cation with a mold cavity 110 through an
injection passage 112 between landing areas 114 and
mold core 78. A circular rib 116 may be provided on
the l~n~; ng area 114 to ~urther restrict the ~low o~
elastomeric material through the passage 112.
Re~erring to Figs 6 and 7, a feed opening 118 is
provided in the extruder cylinder 92 ~or feeding
elastomeric material into the cylinder and a motor 120
is connected to the screw 98 ~or rotating the screw
and mixing the material. As it is mixed, the material
is comml7n;cated by the screw 98 to a centrally located
cavity 124 in the distribution block 88 as shown in
Fig 6. At the same time the extruder 94 is movable
away ~rom the ~ixed press plate 76 with the injection
cylinders 100 to the position shown in Fig 6. Then
hydraulic ~luid is cnmmllnicated to the injection
cylinders 100 causing them to move to the position
shown in Fig 7 and commnn;cate the elastomeric
material ~rom the cavity 124 to the mold cavity 110.
In Figs 8, 9 and 10, the distribution block 88,
cold plate assembly 86, sprue plate 84 and tread mold
as well as an enlarged view o~ one o~ tubes 125 ~or
the ~h~nn~ls 104 are shown. Figs 9 and 10 also
illustrate the con~iguration of the generally spiral
coo~ing passages 126 disposed adjacent the tubes 125.
The passages 126 carry a coolant and extend ~rom an
inlet 127 at a ~irst position 128 upstream ~rom the
mani~old 108 to a second position 130 ~urther upstream
of the mani~old, back to a third position 132 adjacent
the mani~old and then back to the ~irst position where
the coolant is carried away by an outlet 129. In this
manner the elastomeric material being injected through
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the ~h~nn~ls 104 is cooled ~irst at the second
position 130 where it enters the ch~nn~ls with the
lowest temperature coolant and then as the material
passes through the ~h~nn~ls the cooling continues with
coolant which is warmer and does not cause a drop in
material temperature which will adversely a~ect the
curing o~ the elastomeric material a~ter it enters the
mold cavity. In other words, scorching o~ the
material is avoided without causing an undesirable
drop in elastomer temperature.
As shown in Figs 9 and 10, the channels 104 and
cooling passages 126 are each encased in one o~ the
tubes 125 having a spherical end 136 ~or sealing
engagement with a ~emale socket 138 in a distribution
15 block 140. Each tube 125 may have a ~lange 142 with
screws 144 extending through the ~lange and threaded
in the cold plate 86 ~or urging the spherical end 136
into the ~emale socket 138 and thereby provide a seal.
The ~lange 142 may also be bolted to the cold plate 86
20 by screws 145 to hold the tube 125 in sealing
engagement. As shown in Fig 9 a key 147 on the under
side o~ the ~lange 141 is in sliding engagement with a
keyway 149 in the cold plate 86 ~or providing
alignment.
The coolant circulated in the cooling passages
126 may be controlled by a separate cooling system
including a separate pump and th~rmostat to provide
the most desirable coolant temperature and ~low ~or
the elastomer passing through the channels 104.
Furthermore, separate cooling systems may be provided
~or controlling the cooling passages 180 in the
distribution block 140 and cooling passages 24 in cold
plate 86 so that the temperature o~ the injected
elastomer may be controlled at the di~erent locations
to provide high temperatures without scorching ~or
rapid ~low o~ the elastomer.
Re~erring to Fig 12 a stacked mold 150 is shown
which has a distribution plate 151 which may be
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mounted on a fixed press plate 76 of an injection
molding apparatus such as apparatus 65 shown in Figs 6
and 7. The mold 150 has a tapered generally
cylindrical core 152 for supporting a bottom mold
5 plate 153, a top mold plate 154 and intermediate mold
plates 155. Circumferentially spaced runners 156
extend from a nozzle chamber 157 to inlet passages 158
in the core 152 which are in alignment with runner
inlets 160 in the mold plates 153,154 and 155. As
shown in Fig 11, the runner inlets 160 are connected
to a manifold 162 which is connected to a mold cavity
164 by an injection passage 166 defined by a l~n~;ng
area 168 on the respective mold plates 153,154 and 155
spaced from a mating surface 169.
As shown in Figs 12 and 13, the bottom mold plate
153 is fastened to the distribution plate 151 while
the int~rm~;~te mold plates 155 and top mold plate
154 may be lifted off the core 146 for removal of a
molded tire component such as bead apex assembly 170
from the mold cavity 164. The number of molded tire
components to be molded at one time can be changed by
increasing or decreasing the thickness of the bottom
mold plate 153 and adding or decreasing the number of
intermediate mold plates 155.
Referring to Fig 14, the top mold plate 154 is
shown a~ter opening o~ the stacked mold 150 showing
the bead apex assembly 170 after injection and still
ret~;n~ in the mold cavity 164. An unloader ring 172
is movable into a position abutting the bead apex
30 assembly 170 and may have sealing rings 174 at the
edges for engagement with the surface of the assembly
170. A plurality of circumferentially spaced apart
openings 176 in the ring 172 disposed between the
sealing rings 174 are in commnn;cation with a source
of vacuum through passages 178. In operation a vacuum
is cnmmlln;cated to the passages 178 for pulling the
bead apex assembly 170 out o~ the mold cavity 164
against the unloader ring 172 without distorting the
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assembly. The unloader ring 172 iS then movable to a
position spaced ~rom the top mold plate 154 where the
assembly may be stored or used to build a tire. This
same unloader ring 172 may be used in conjunction with
the intermediate mold plates 155 of the embodiment
shown in Fig 12 or with the upper mold half 14 of the
embodiment shown in Fig 1. In this m~nn~ this tire
component which is partially vulcanized may be removed
from the mold and handled without distortion which is
important for ~abricating a high precision tire.
The invention has been described with reference
to a preferred embodiment. Obviously, modi~ications
= and alterations will occur to others upon a reading
and underst~n~;ng of this specification. It is
intended to include all such modifications and
alterations insofar as they come within the scope o~
the appended claims or the equivalents thereo~.
